the ankle brachial index measurement, calculation, and interpretation limitations ivan casserly md...

The Ankle Brachial IndexThe Ankle Brachial IndexMeasurement, Calculation, and InterpretationMeasurement, Calculation, and Interpretation

LimitationsLimitations

Ivan Casserly MDIvan Casserly MD

Denver VA Medical CenterDenver VA Medical CenterUniversity of Colorado HospitalUniversity of Colorado Hospital

Ankle Brachial IndexAnkle Brachial Index

• Ankle brachial index (ABI)Ankle brachial index (ABI)

• Ankle brachial pressure index (ABPI)Ankle brachial pressure index (ABPI)

• Ankle arm index (AAI)Ankle arm index (AAI)

Ankle Brachial IndexAnkle Brachial IndexWhy should we care?Why should we care?

• In clinical practiceIn clinical practice

– Aids in diagnosis and assessment of patients with Aids in diagnosis and assessment of patients with symptoms suggestive of PADsymptoms suggestive of PAD

– Role in primary prevention since PAD is a powerful Role in primary prevention since PAD is a powerful independent predictor of CV morbidity and mortality independent predictor of CV morbidity and mortality regardless of symptomatic status of PAD. regardless of symptomatic status of PAD.

Ankle Brachial IndexAnkle Brachial IndexHow good is it at diagnosing PAD?How good is it at diagnosing PAD?

• Using gold standard of DSA angiography Using gold standard of DSA angiography

– >50% stenosis in lower extremity vessel >50% stenosis in lower extremity vessel

Ankle Brachial IndexAnkle Brachial IndexDiagnosis of PAD Diagnosis of PAD

0

10

20

30

40

50

60

70

80

90

Sensitivity Specificity Accuracy

HAP

Niazi et al, Cath Cardiovasc Interv 2006;68:788-792

Ankle Brachial IndexAnkle Brachial IndexRole in Primary Prevention – Low incidence of classic claudicationRole in Primary Prevention – Low incidence of classic claudication

PADPAD

ClaudicationClaudicationAtypical SymptomsAtypical SymptomsAsymptomaticAsymptomatic

StableStablePADPAD Rest PainRest Pain Tissue LossTissue Loss

CLI

Peripheral Arterial DiseasePeripheral Arterial DiseasePrevalencePrevalence

• PARTNERS Program (PAD Awareness, Risk, and Treatment: PARTNERS Program (PAD Awareness, Risk, and Treatment: New Resources for Survival)New Resources for Survival)

– 350 Primary care sites 350 Primary care sites – Patients (n=~7,000)Patients (n=~7,000)

• >70 yrs >70 yrs • 50-69 yrs with history DM or smoking50-69 yrs with history DM or smoking

– PVD diagnosisPVD diagnosis• ABI <0.9ABI <0.9• Previous documentationPrevious documentation• Abnormal vasc studiesAbnormal vasc studies• Prior revascularizationPrior revascularization

Hirsch AT, JAMA 2001;286:1317-1324Hirsch AT, JAMA 2001;286:1317-1324

Peripheral Arterial DiseasePeripheral Arterial DiseasePrevalencePrevalence

0

5

10

15

20

25

%

PVD CVD PVD + CVD

13%

24%

16%

Hirsch AT, JAMA 2001;286:1317-1324Hirsch AT, JAMA 2001;286:1317-1324

Peripheral Arterial DiseasePeripheral Arterial DiseaseUnder-diagnosis in Primary Care Practice / Influence of assoc. diagnosis of CVDUnder-diagnosis in Primary Care Practice / Influence of assoc. diagnosis of CVD

0

2

4

6

8

10

12

%

PVD PVD + CVD

New

Prior7%

6% 6%

10%

Hirsch AT, JAMA 2001;286:1317-1324Hirsch AT, JAMA 2001;286:1317-1324

Adapted from Criqui MH, et al. N Engl J Med. 1992;326:381-386.Adapted from Criqui MH, et al. N Engl J Med. 1992;326:381-386.

Normal Subjects

Asymptomatic PAD

Symptomatic PAD

Severe Symptomatic PAD Su

rviv

al

Year

1.00

1210864200.00

0.25

0.50

0.75

Peripheral Arterial DiseasePeripheral Arterial DiseaseImpact of Diagnosis on Survival Impact of Diagnosis on Survival

Resnick et al. CirculationResnick et al. Circulation 2004;109;733-7392004;109;733-739

Peripheral Arterial DiseasePeripheral Arterial DiseaseImpact of Diagnosis on SurvivalImpact of Diagnosis on Survival

Peripheral Arterial DiseasePeripheral Arterial DiseaseImpact of Diagnosis on Survival – Polyvascular DiseaseImpact of Diagnosis on Survival – Polyvascular Disease

0

5

10

15

20

25

30

All-cause Mortality CV death Nonfatal MI CV death, MI,stroke, or

hospitalization

%

PAD alone PAD +CVD PAD + CHD PAD + CHD + CVD

Adapted from PG Steg et al. JAMA.2007;297:1197-1206.

ABI and Primary PreventionABI and Primary PreventionAlgorithmAlgorithm

Doobay AV et al. Arterioscler Thromb Vasc Biol.2005;25:1463-1469.

Ankle Brachial IndexAnkle Brachial Index

• PerformancePerformance

• CalculationCalculation

• InterpretationInterpretation

Ankle Brachial IndexAnkle Brachial IndexPerformance - EquipmentPerformance - Equipment

Ankle Brachial Index Ankle Brachial Index PerformancePerformance

Hiatt WR, N Engl J Med 2001;344:1608-1621

Ankle Brachial IndexAnkle Brachial IndexPerformancePerformance

• CLINICAL DEMONSTRATIONCLINICAL DEMONSTRATION

Ankle Brachial IndexAnkle Brachial IndexPerformance - ReviewPerformance - Review

• Patient PositionPatient Position

– No activity for 4-5 minutesNo activity for 4-5 minutes

– Supine positionSupine position

Ankle Brachial IndexAnkle Brachial IndexPerformance – Arm PressurePerformance – Arm Pressure

• Arm Arm

– Appropriate cuff sizeAppropriate cuff size

– Doppler over brachial arteryDoppler over brachial artery

• NOT STETHESCOPE (underestimate SBP)NOT STETHESCOPE (underestimate SBP)

• NOT OVER RADIAL ARTERYNOT OVER RADIAL ARTERY

– Record right AND left arm brachial pressuresRecord right AND left arm brachial pressures

• Why?Why?

Ankle Brachial IndexAnkle Brachial IndexPerformance – Ankle PressurePerformance – Ankle Pressure

• CuffCuff

– Appropriate sizeAppropriate size

– Appropriate locationAppropriate location

• Lower leg above malleoliLower leg above malleoli

• NOT OVER BULK OF CALF MUSCLESNOT OVER BULK OF CALF MUSCLES

• Doppler over DP AND PTDoppler over DP AND PT

– NOT STETHESCOPENOT STETHESCOPE

Ankle Brachial IndexAnkle Brachial IndexCalculationCalculation

• ABIABI

– Numerator – Ankle pressuresNumerator – Ankle pressures

• Higher of the two pedal pressuresHigher of the two pedal pressures

• BrachialBrachial

– Denominator – Brachial pressureDenominator – Brachial pressure

– Higher of the two arm pressuresHigher of the two arm pressures

– Best reflects aortic pressureBest reflects aortic pressure

Ankle Brachial IndexAnkle Brachial IndexCalculation - RationaleCalculation - Rationale

• Method 1. Method 1.

– Higher of the two Higher of the two pressurespressures

– ABI 150/150 = 1ABI 150/150 = 1

• Sensitivity ↓Sensitivity ↓

• Specificity ↑Specificity ↑

• Method 2. Method 2.

– Lower of the two Lower of the two pressurespressures

– ABO 100/150 = 0.66ABO 100/150 = 0.66

• Sensitivity ↑Sensitivity ↑

• Specificity ↓Specificity ↓

• PatientPatient

– DP 100, PT 150, Highest brachial 150DP 100, PT 150, Highest brachial 150

Ankle Brachial IndexAnkle Brachial IndexHigh versus Low Ankle Pressure (HAP vs LAP) High versus Low Ankle Pressure (HAP vs LAP)

0

10

20

30

40

50

60

70

80

90

Sensitivity Specificity Accuracy

HAP

LAP

Niazi et al, Cath Cardiovasc Interv 2006;68:788-792

Ankle Brachial IndexAnkle Brachial IndexInterpretationInterpretation

• What is a normal ABI?What is a normal ABI?

Ankle Brachial IndexAnkle Brachial IndexInterpretationInterpretation

• Normal ankle pressure is 8-15% higher than arm Normal ankle pressure is 8-15% higher than arm pressurepressure

• Epidemiological studies have used ABI of 0.9 as cutoff Epidemiological studies have used ABI of 0.9 as cutoff of normal from abnormal for diagnosis of PAD. of normal from abnormal for diagnosis of PAD.

Ankle Brachial IndexAnkle Brachial IndexInterpretation – High ABI – Non-compressible vessels Interpretation – High ABI – Non-compressible vessels

Ankle Brachial Index Ankle Brachial Index InterpretationInterpretation

ABI Interpretation >1.3 Non-compresssible 1.00 - 1.29 Normal 0.91 - 0.99 Equivocal 0.41 - 0.90 Mild-to-moderate PVD 0.00 - 0.40 Severe PVD

Hirsch AT et al, J Am Coll Cardiol 2006;47:1239-1312

StudyStudy

• 17 volunteers17 volunteers

– 11stst year n=10 year n=10

– 22ndnd year n=4 year n=4

– 33rdrd year n=3 year n=3

Feedback from StudyFeedback from StudyPart A – Performance of ABIPart A – Performance of ABI

• Measure ABI for right leg on Measure ABI for right leg on patientpatient

Measure Right ABIMeasure Right ABIFeedback – Arm MeasurementFeedback – Arm Measurement

0

20

40

60

80

100

%

Cuff size Rt and Lt Brachial Doppler

Correct

N=1N=2

N=15

Measure Right ABIMeasure Right ABIFeedback – Leg MeasurementFeedback – Leg Measurement

0

20

40

60

80

100

%

Cuff size CuffLocation

DP and PT Doppler*

Correct

N=1N=3

N=8N=9

* Obtained accurate Doppler signal from DP and PT

Feedback from StudyFeedback from StudyPart B – Calculation of ABIPart B – Calculation of ABI

• Right brachialRight brachial

• Left brachialLeft brachial

• Right PTRight PT

• Right DPRight DP

• Left PTLeft PT

• Left DPLeft DP

• AA

• BB

• CC

• DD

• EE

• FF

150mmHg150mmHg

140mmHg140mmHg

100mmHg100mmHg

130mmHg130mmHg

120mmHg120mmHg

105mmHg105mmHg

Right ABI = D/ALeft ABI = E/A

ABI Calculation ABI Calculation FeedbackFeedback

• ErrorsErrors

– Brachial:Ankle indexBrachial:Ankle index

– Same leg/armSame leg/arm

• Right ankle/right armRight ankle/right arm

• Left ankle/left armLeft ankle/left arm

– Lower brachial pressureLower brachial pressure

– Use of DP aloneUse of DP alone

– Use of PT aloneUse of PT alone

0

20

40

60

80

100

%

ABI calculation

Correct

N=1

Feedback from StudyFeedback from StudyPart C – Interpretation of ABIPart C – Interpretation of ABI

• A – non-compressibleA – non-compressible

• B – normalB – normal

• C – mildC – mild

• D – ModerateD – Moderate

• E - SevereE - Severe

• ABIABI

– 1.61.6

– 1.21.2

– 1.01.0

– 0.80.8

– 0.40.4

ABI Interpretation ABI Interpretation FeedbackFeedback

0

20

40

60

80

100

%

ABIinterpretation

Correct

N=7

Ankle Brachial Index Ankle Brachial Index InterpretationInterpretation

ABI Interpretation >1.3 Non-compresssible 1.00 - 1.29 Normal 0.91 - 0.99 Equivocal 0.41 - 0.90 Mild-to-moderate PVD 0.00 - 0.40 Severe PVD

Ankle Brachial IndexAnkle Brachial IndexLimitationsLimitations

• Localization of diseaseLocalization of disease

• Non-compressible ABINon-compressible ABI

• Pseudo-normal ABIPseudo-normal ABI

• Resting versus exercise ABIResting versus exercise ABI

• Role in diagnosis of critical limb ischemia (CLI)Role in diagnosis of critical limb ischemia (CLI)

• Hypertensive patientHypertensive patient

ABI and Localization of DiseaseABI and Localization of DiseaseSegmental Limb PressuresSegmental Limb Pressures

BrachialBrachial

Upper ThighUpper Thigh

Upper CalfUpper Calf

AnkleAnkle

ToeToe

Aorto-Iliac, CFA, Prox SFAAorto-Iliac, CFA, Prox SFA

Mid/distal SFA and PoplitealMid/distal SFA and Popliteal

TibialTibial

Small Vessel DiseaseSmall Vessel Disease

ABI and Localization of DiseaseABI and Localization of DiseasePulse Volume RecordingsPulse Volume Recordings

• Measures volume change in Measures volume change in limb with each pulsationlimb with each pulsation

• Volume of tissue and venous Volume of tissue and venous blood relatively constantblood relatively constant

• Change in volume due to Change in volume due to arterial inflowarterial inflow

• Cuffs inflated to ~60mmHgCuffs inflated to ~60mmHg

• Volume change presented on Volume change presented on spectral displayspectral display

• Similar to arterial pulse wave Similar to arterial pulse wave tracingtracing

• Stenosis indicated by loss of Stenosis indicated by loss of amplitude during systoleamplitude during systole

Non-Compressible ABINon-Compressible ABI

Non-Compressible ABIsNon-Compressible ABIsRole of Toe PressureRole of Toe Pressure

• Toe Pressure Toe Pressure

– Great toeGreat toe 32mHg32mHg

– 22ndnd toe toe 35mmHg35mmHg

– 33rdrd toe toe17mmHg17mmHg

– 44thth toe toe 19mmHg19mmHg

– 55thth toe toe absentabsent

•Normal toe-brachial index > 0.7Normal toe-brachial index > 0.7

Non-invasive Hemodynamic EvaluationNon-invasive Hemodynamic EvaluationToe PressureToe Pressure

Pseudonormal ABIPseudonormal ABI

PAD

Vessel Ca 2+

ABI

Resting versus Exercise ABIResting versus Exercise ABIExercise TestingExercise Testing

• Exercise Exercise

– ABI at baselineABI at baseline

– 2 mph at 12% grade, 5 2 mph at 12% grade, 5 minutesminutes

– ABI post-exercise, 1 minute, ABI post-exercise, 1 minute, then q 2 minutesthen q 2 minutes

• Post-exercise ankle systolic Post-exercise ankle systolic pressure pressure

– Falls >20% from baselineFalls >20% from baseline

– Takes longer than 3 minutes Takes longer than 3 minutes to recoverto recover

Resting versus Exercise ABIResting versus Exercise ABIExercise TestingExercise Testing

0

20

40

60

80

100

%

Normal Abnormal Non-compressible

ABI

0

20

40

60

80

100

%

ExerciseNormal

ExerciesAbnormal

Resting ABIResting ABI Exercise ABIExercise ABI

N=396 symptomatic patients with PAD.N=396 symptomatic patients with PAD.

Resting versus Exercise ABIResting versus Exercise ABIExercise TestingExercise Testing

• 58 year old male58 year old male

• Right buttock claudicationRight buttock claudication

– Classic descriptionClassic description

Non-invasive Hemodynamic EvaluationNon-invasive Hemodynamic EvaluationExercise TestingExercise Testing

Delete

Delete n=49

ABI in Patients with Critical Limb IschemiaABI in Patients with Critical Limb IschemiaLimitationLimitation

ABIABI

ABI in Patients with Critical Limb IschemiaABI in Patients with Critical Limb IschemiaImportance of Indication for AssessmentImportance of Indication for Assessment

Lower Extremities Test DEC 14,2005@14:00 SEGMENTAL LIMB PRESSURE (mm Hg) PVR (CATEGORY-AMPLITUDE) RIGHT LEFT RIGHT LEFT RESTING LEVELS 142 138 BRACHIAL 1-92 1-49 160 170 THIGH 1-50 1-50 152 150 CALF 1-60 1-78 140 (0.99) 160 (1.13) ANKLE 2-16 1-35 TM 2.5 2-26 2-21 92 110 TOE 5.0

Right HeelRight Heel

Ankle Pressure 140mmHgABI 0.99Toe Pressure 92mmHg

Popliteal and Tibial AngiographyPopliteal and Tibial Angiography

ATAT

ATAT

PTPT

PTPT

PeronealPeroneal

PeronealPeroneal

ConclusionsConclusions

• ABI ABI

– Helpful in diagnosis and assessment of patients Helpful in diagnosis and assessment of patients with symptomatic PADwith symptomatic PAD

– Useful in primary prevention of CV morbidity and Useful in primary prevention of CV morbidity and mortality, especially in asymptomatic patients or mortality, especially in asymptomatic patients or patients with atypical symptoms. patients with atypical symptoms.

– Requires training in order to perform correctly and Requires training in order to perform correctly and calculate ABIcalculate ABI

– Has limitations that should be understoodHas limitations that should be understood